Seasonal Variation in Testis-Stimulating Activity of Male Pheasant Pituitary Glands

Abstract

THIS paper is a study of seasonal pituitary-gonad relationships in game farm Ring-necked Pheasants (Phasianus colchicus). Investigations of the seasonal breeding physiology of birds have customarily been approached through study of gonadial activity. The data obtained in this way are abundant, but there is little information on the seasonal variation in gonadotrophic activity of the pituitary gland, measured by direct means. In this paper we shall present data from the bio-assay of gonadotrophin in dried pheasant pituitary gland collected monthly throughout the year. Burger (1949) emphasized the need for further direct work on the pituitary gland as the master control of breeding activity. How closely the quantity of gonad-stimulating hormone produced by the pituitary gland follows the seasonal changes in gonadial activity has not been shown. Seasonal changes in the gonads may be due to parallel changes in pituitary pro;luction of gonadotrophic hormone or may reflect changes in the sensitivity of the gonads themselves to this hormone. No data on the level of gonadotrophic hormone in the pituitary gland or the blood stream at various seasons of the year are available. However, the presence of gonad-stimulating substances in the pituitary gland has been demonstrated in most domestic birds, and Benoit (1935) demonstrated that the amount of these substances increased in the pituitaries of ducks which were subjected to increased day-length. Phillips (1942) found no gonad-stimulating activity in the pituitary gland of the Ring-necked Pheasant but did not state at what season the material was obtained. A higher level of pituitary gonadotrophin has been demonstrated in older and reproductively more active male chickens and pigeons than in younger, inactive individuals (Breneman, 1944; Kato, 1938; Schooley, 1937; Smith and Engle, 1927). In domestic hens, on the other hand, more pituitary gonadotrophin was shown in non-laying than in laying birds (Phillips, op. cit.; Riley and Fraps, 1942). The answers to some of these problems can be surmised from what is known, but direct evidence is fragmentary. This study was supported by a grant-in-aid from the Wisconsin Alumni Research Foundation, and the birds and facilities of the Experimental Game and Fur Farm at Poynette, Wisconsin, were provided by the Wisconsin Conservation Department. Mr. Cyril